1. Field of the Invention
The invention relates to the engineering of plants to alter lipid content in vegetative portions of the plant.
2. Description of Related Art
Plants synthesize and store oil primarily in cytosolic lipid droplets, and much of the Earth's fossil fuel reserves are the consequence of this process. In domesticated oilseeds, these stored triacylglycerols (TAGs) represent a major source of calories for human and animal nutrition, an excellent feedstock for diesel fuels, and a reservoir for the deposition of industrial fatty acids for chemical feedstocks. A number of acyltransferases are involved in the biosynthesis of TAGs, including acyl-CoA:cholesterol acyltransferases (ACATs), diacylglycerol acyltransferases (i.e., DGAT1s and DGAT2s), lecithin:cholesterol acyltransferases (LCATs), phospholipid:diacylglycerol acyltransferases (PDATs), glycerol-3-phosphate acyltransferases (GPATs) and acyl-CoA lysophosphatidic acid acyltransferases (LPAATs). In plants, TAG is the primary component of vegetable oil that is used by the seed as a stored form of energy to be used during seed germination.
Higher plants are believed to synthesize oils via a metabolic pathway commonly referred to as the Kennedy pathway (Kennedy et al., 1956; Finnlayson et al., 1980). Fatty acids are made in plastids from acetyl-CoA through a series of reactions catalyzed by enzymes known collectively as Fatty Acid Synthase (FAS). The fatty acids produced in plastids are exported to the cytosolic compartment of the cell, and are esterified to coenzyme A. These acyl-CoAs are the substrates for glycerolipid synthesis on the endoplasmic reticulum (ER). Glycerolipid synthesis itself is a series of reactions leading first to phosphatidic acid (PA) and 1,2-diacylglycerol (DAG). Either of these metabolic intermediates may be directed to membrane phospholipids such as phosphatidylglycerol (PG), phosphatidylethanolamine (PE), or phosphatidylcholine (PC), or they may be directed on to form neutral triacylglycerol (TAG). DAG is synthesized from glycerol-3-phosphate and fatty acyl-CoAs in two steps catalyzed sequentially by glycerol-3-phosphate acyltransferase (G3PAT), and lysophosphatidic acid acyltransferase (LPAAT) to make PA, and then an additional hydrolytic step catalyzed by phosphatidic acid phosphatase (PAP) to make DAG. In most cells, DAG is used to make membrane phospholipids, the first step being the synthesis of PC catalyzed by CTP-phosphocholine cytidylyltransferase. In cells producing storage oils, DAG is acylated with a third fatty acid in a reaction catalyzed by DAGAT.
Factors governing the oil content of a vegetative plant part are not well known, and the role of a CGI58 homolog in lipid accumulation in vegetative tissues of plants has not been previously described. As such, materials and methods for increasing the neutral lipid (e.g. oil content, including TAG) content in cells of plant vegetative tissues by use of CGI58-related sequences have not been previously described.